As an electronic control unit, there is known an electronic control unit including a printed circuit board (hereinafter, also simply referred to as a board) on which a semiconductor device is mounted for an automobile, a construction machine and the like. The semiconductor device mounted on the board is connected to an electronic component such as another semiconductor device by a wiring pattern formed on the board. Operation of the semiconductor device generates an operation current, and unwanted emission noise is generated from the semiconductor device and/or the wiring pattern due to the operation current. That is, the unwanted emission noise is generated from the board.
The emission noise is desired to be low so as not to affect other equipment, and an allowable level of emission noise is standardized by Comite International Special des Perturbations Radioelectriques (CISPR) that is a special committee of International Electrotechnical Commission (IEC). For example, an allowable level of emission noise from a component module mounted in an automobile is specified for a frequency up to 960 MHz in Non-Patent Document 1.
In order to reduce the emission noise from the board, a technique using a shield case that covers the board is used. In this case, the board is, for example, accommodated in the shield case and is provided as an electronic control unit. In the technique using the shield case, a resonance phenomenon occurs at a specific frequency (resonance frequency) depending on the size of the shield case. Therefore, shielding performance is lowered at the resonance frequency, and the emission noise from the shield case to outside may become large.
Patent Document 1 discloses a notch that is provided along a ridgeline of an upper surface and a side surface of the shield case so that the emission noise from the board and the resonance frequency of the shield case do not coincide.